The purpose of this research project is concurrent investigation of multiple, time varying physiologic functions in healthy adult subjects at three different ages, 21 to 30, 50 to 65 and 65 to 80, living in an environment free of time cues. We will determine whether interindividual differences occur, and whether they vary systematically as a function of age or previous habitual 24 hour behavior patterns (i.e., "Morning" and "Evening," "long" and "short" sleeping individuals). We also plan to pursue three other lines of investigation. The first is the study of the effect of the light-dark cycle as an entraining agent. Second, we will continue to study, by a specific set of experimental manipulations, the relationship between the circadian rhythm of core body temperature and both the sleep period length and the internal organization of sleep stages during a night. Third, we will study two groups of patients living in the environment free of time cues: chronic insomniacs and narcoleptics. Studying such patients under these conditions will yield important information contributing to our understanding of these two serious functional disorders which affect greater than 20 million people in the United States.